The present invention relates generally to automotive electrical power systems, and more particularly, to a replacement battery formation system.
Most of today""s motor vehicles carry an internal combustion engine that functions optimally at high speeds only. It is by necessity larger than an engine required for xe2x80x9cin townxe2x80x9d operation. Therefore a penalty is paid for the luxury of broad range operation, including the deterioration of our environment. Emissions during warm-up, low speed, and idle operations are not negligible. A large engine requires longer warm-up time, and short trips may not achieve warm-up in many cases, increasing the pollution problem.
There exists, at the moment, much effort in addressing the basic need for an efficient power source at all operating conditions. One such effort, known as electric vehicle, approaches the problem by carrying an on-board bank of batteries for an electric drive mechanism. Unfortunately, replacement of one battery module in a string of traction battery modules requires that the replacement battery be matched in terms of polarization properties. New batteries are typically not usually fully formed, so a number of xe2x80x9cbreak-inxe2x80x9d discharge-charge cycles are performed to complete the formation.
The lead-acid battery formation process involves the conversion of lead oxide and sulfates to concentrated acid in the electrolyte and lead dioxide and porous lead metal on the electrodes. This is accomplished through repeated forced charges and discharges, with each cycle adding to the reservoir of active material. The net result of the formation process is that the charge voltage, which is a function of acid concentration and plate characteristics, is in a period of continual adjustment during formation.
The formation process is time and energy consuming and is often circumvented by only forming the batteries to the point where they are serviceable but not optimized. Then, normal charge and discharge during customer use is used to complete formation.
Economics of electric vehicles, however, requires service to individual cells in the battery string. If a newly produced (under-formed) cell is placed in a well-cycled battery string, the different charge voltage will cause difficulties in charging. Currently, the solution is to produce a stock of replacement cells that have been cycled at least twenty times (to the completely formed state), which presents a substantial cost and time burden. Also, no simple metric exists to determine when formation is complete so it is possible that under-formed cells will be released for customer use.
The disadvantages associated with these conventional replacement battery formation techniques have made it apparent that a new technique for battery formation is needed. The new technique should be capable of providing a means to determine when a battery is fully formed. Additionally, the new technique should be capable of preventing over cycling or under cycling of replacement batteries. The present invention is directed to these ends.
It is, therefore, an object of the invention to provide an improved and reliable replacement battery formation system. Another object of the invention is to provide a means to determine when a battery is fully formed. Additionally, the new technique should be capable of preventing over cycling or under cycling of replacement batteries.
In accordance with the objects of this invention, a replacement battery formation system is provided. In one embodiment of the invention, a replacement battery formation method includes the steps of; providing a bank of batteries made up of a plurality of individual batteries having substantially the same state of formation; cycling a replacement battery by forcing repeated charging and discharging; monitoring a formation state of the replacement battery; ending the cycling when the replacement battery has approximately the same formation state as the plurality of individual batteries; and replacing one of the plurality of batteries with the replacement battery.
The present invention thus achieves an improved replacement battery formation system. The present invention is advantageous by preventing the over cycling (leading to reduced life and greater cost) or under cycling (leading to defective batteries) of replacement batteries.
Additional advantages and features of the present invention will become apparent from the description that follows, and may be realized by means of the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings.